472 PROCEEDINGS OF THE NATIONAL MUSEUM vol.88 



The first maxillae have reached the highest point of development as 

 a clasping organ and in the next stages will begin to degenerate. The 

 boundary between the basal and second segments is becoming in- 

 distinct, two spines on the second segment have disappeared, and the 

 framework of the suction cup is faintly seen within the basal segment. 

 On the second maxillae a small spine has been added to the basal 

 segment at the posterior distal corner (the outer spine of the adult) , 

 and some minute spinules have made their appearance. 



A few spinules occur for the first time on the ventral surface in 

 front of the anterior marginal groove and along the margin of the 

 carapace adjacent to the anterior respiratory area. Rudiments of the 

 flagella are formed on the posterior dorsal corner at the base of the 

 exopod of the two anterior pairs of swimming legs. On the female 

 a minute chitinous spine appears at the extremity of the duct of the 

 seminal receptacle. 



Fourth stage. — A larva seven to eight days old molts for a third 

 time and has reached a length of 1.2 to 1.4 mm. The lateral lobes of 

 the carapace barely cover the second swimming appendages. Branches 

 of the lateral groove limiting the cephalic area are faintly seen extend- 

 ing inward. The anterior dorsal ribs show a rudimentary outer 

 branch, and the ciliary fringe of the carapace extends as far back as 

 the second maxillae. 



Both pairs of antennae are the same as in the previous stage, but 

 the buccal fold of the proboscis has two teeth on the free margin. 

 On the basal segment of the first maxillae there is a considerable 

 expansion due to the formation of the suction cup. The circular 

 margin is fringed with minute triangular processes, and the muscles 

 attached to it can be seen through the chitinous exoskeleton. Buds of 

 the flagella on the first two pairs of thoracic appendages are still very 

 small and without any setae. On the male the posterior side of the 

 joint between the coxa and basis of the third leg is deeply cut where 

 it foreshadows the socket of the adult. The abdomen of the female 

 is slightly smaller than that of the male. 



Fifth stage. — Three to four days after the third ecdysis a fourth 

 molt occurs, and the larva reaches 1.3 to 1.7 imn. in length. The 

 outer branches of the dorsal ribs are still short and the ciliated mar- 

 gin of the carapace has extended almost to the first thoracic segment. 



The two basal segments of the second antennae have several setae 

 on the distal end. The third segment is small, the fourth twice as 

 long as the third, with the two setae that occurred on the segment in 

 the preceding stages moved to the distal end. The last segment is as 

 long as the fourth and is tipped with a few rather thick setae. 



The labial spines are distinctly located on the floor of the buccal 

 cavity. Important changes have also occurred in the first maxillae. 



